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#5: Post edited by

alx‭ · 2025-10-30T12:46:32Z (11 months ago)

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I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to set different traps for different parts of a pipeline?
~~Alternatively, I guess I could entirely disable `set -Ee`, and inspect PIPESTATUS for each command, but I was hoping for something simpler.~~

I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to set different traps for different parts of a pipeline?
Alternatively, I guess I could entirely disable `set -Ee`, and inspect PIPESTATUS for each command, but I was hoping for something simpler. Also, the real script is much more complex, and I think PIPESTATUS would be impractical, so I'd probably fall back to `grep || true` and say my script also returns 0 if nothing matched, unlike grep(1).

#4: Post edited by

alx‭ · 2025-10-30T12:44:15Z (11 months ago)

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I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to set different traps for different parts of a pipeline?
~~Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.~~

I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to set different traps for different parts of a pipeline?
Alternatively, I guess I could entirely disable `set -Ee`, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

#3: Post edited by

alx‭ · 2025-10-30T12:39:47Z (11 months ago)

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I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
~~Is there a way to untrap only part of a pipe?~~
Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to set different traps for different parts of a pipeline?
Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

#2: Post edited by

alx‭ · 2025-10-30T12:38:59Z (11 months ago)

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I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to untrap only part of a pipe?
Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.
But I don't find a way to do it. So far, I've written this:
```bash
alx@devuan:~/tmp/g$ ls
file file2 script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2
qwe
xcsv
```
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```
If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.
If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.
```bash
alx@devuan:~/tmp/g$ cat script
#!/bin/bash
set -Eeuo pipefail;
#shopt -s lastpipe;
trap 'exit 2;' ERR;
if test -z "$*"; then
trap 'exit 1' ERR;
grep foo;
else
find "$@" -type f \
| {
trap 'exit 1' ERR;
xargs grep foo;
};
fi;
```
```bash
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```
Is there a way to untrap only part of a pipe?
Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

#1: Initial revision by

alx‭ · 2025-10-30T12:38:14Z (11 months ago)

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How to pipe grep(1) and use compatible exit codes?

I need to wrap grep(1) in a script, and I'd like the script to have an exit code compatible with that of grep(1) --that is, it should return 0 if it found something, 1 if it didn't, and 2 on error--.

But I don't find a way to do it.  So far, I've written this:

```bash
alx@devuan:~/tmp/g$ ls
file  file2  script
alx@devuan:~/tmp/g$ cat file
foo
bar
alx@devuan:~/tmp/g$ cat file2 
qwe
xcsv
alx@devuan:~/tmp/g$ cat script 
#!/bin/bash

set -Eeuo pipefail;
shopt -s lastpipe;

trap 'exit 2;' ERR;

if test -z "$*"; then
	trap 'exit 1' ERR;
	grep foo;
else
	find "$@" -type f \
	| {
		trap 'exit 1' ERR;
		xargs grep foo;
	};
fi;
alx@devuan:~/tmp/g$ echo foo | bash script; echo $?
foo
0
alx@devuan:~/tmp/g$ echo bar | bash script; echo $?
1
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
1
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
1
```

If find(1) fails, it uses the trap handler set next to grep(1), probably because pipes are executed in parallel, and because lastpipe makes the trap(1) be executed in the same shell.

If I change the script to not use lastpipe, then that is fixed (find(1) errors are properly transformed into code 2), but then when grep(1) doesn't find anything it also is treated as an error with code 2.

```bash
alx@devuan:~/tmp/g$ cat script 
#!/bin/bash

set -Eeuo pipefail;
#shopt -s lastpipe;

trap 'exit 2;' ERR;

if test -z "$*"; then
	trap 'exit 1' ERR;
	grep foo;
else
	find "$@" -type f \
	| {
		trap 'exit 1' ERR;
		xargs grep foo;
	};
fi;
alx@devuan:~/tmp/g$ bash script file; echo $?
foo
0
alx@devuan:~/tmp/g$ bash script file2; echo $?
2
alx@devuan:~/tmp/g$ bash script file3; echo $?
find: ‘file3’: No such file or directory
2
```

Is there a way to untrap only part of a pipe?

Alternatively, I guess I could entirely disable `set -Ee` in that part of the script, and inspect PIPESTATUS for each command, but I was hoping for something simpler.

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